Wireless Channels: The Jargon Demystified
The most overused jargon in wireless microphones explained...
Wireless microphones are still a relatively new technology and have adopted certain terminologies from other areas of the audio industry to describe how they work. Unfortunately, these terminologies do not always translate smoothly. For example, the word 'channel' – while relatively simple to understand outside of wireless – has three different meanings in a wireless context, and understandably, this can be confusing.
'What group and channel is that channel operating on?' or 'how many channels can you get in a TV channel?' are both completely valid questions, and those used to working with radio microphones and In-Ear Monitoring systems will understand them perfectly. But, what about the rest of us? Well, here's an explanation…
What on Earth Is a Channel Anyway?
In simple terms, a channel is a means of directing something toward a particular end or object. Or, in other words, a means of getting something from one point to another (perhaps through a specified route or medium). It describes both an 'end-to-end' system – like a wireless microphone and a receiver – and also the route between the two items. (i.e., the range of frequencies that the end-to-end system uses to transmit data.)
The following are examples of the many wireless 'channels' in context:
1. 'A Channel of Wireless'
A combination of 1 wireless transmitter and 1 receiver is equal to a single channel of wireless. Likewise, 10 transmitters and 10 receivers would equal 10 channels in total. Things start to get confusing, however, when introducing physical receiver units that can receive more than 1 channel simultaneously. Such units are typically dual or quad channel receivers. For example, 4 transmitters and 1 quad receiver gives you 4 channels of wireless. Or, 8 transmitters, 1 quad receiver, and 2 dual receivers gives you 8 channels.
The principle is identical for In-Ear Monitoring systems, but this time, the transmitters are the stationary item, and the receivers are worn on the body. In this case, transmitters are available as either single channel or dual channel. So, 10 dual channel transmitters and 20 bodypack receivers equates to 20 channels of wireless.
2. TV Channels
Most radio microphones use UHF (Ultra High Frequency) radio spectrum. Explaining why we use this spectrum is beyond the scope of this document, but the part we're interested in is bands IV and V - covering 470-854 MHz. To better explain who or what uses which chunk of this spectrum, it was subdivided into 8MHz wide blocks ready to be allocated to different users. It's like slicing up an entire French stick ready for diners to spread their preferred pâté or cheese on. Mmmm cheese.....
The primary user of this spectrum was TV broadcast, and so each 8 MHz slice of spectrum was given a TV Channel number and was initially used for a single analogue transmission. For example, BBC1 in London may have been broadcast on TV Channel 24 (494-502 MHz). With modern Digital Television, TV Channel 24 (494-502 MHz) may now carry more than just BBC1.
Tuning Bandwidth / Frequency Range
Frequency Range, or Tuning Bandwidth refers to the range of frequencies a radio mic system can tune to. It can be a small range covering 24 MHz / 3 TV channels (Remember that 3 TV channels @ 8 MHz each = 24 MHz) or even up to 64 MHz / 8 TV channels.
3. Groups and Channels
Radio mics shouldn't be tuned randomly to arbitrary frequencies, as it can result in interference between your own radio mics – not an ideal situation. For this reason, Shure pre-program Groups and Channels. A Channel in a Group will refer to a spot, or fixed, frequency. For example, Group 1, Channel 1 could be 606.700 MHz. Group 1 Channel 2 could be 607.175 MHz.
Now here's the clever bit; ignoring any possibility of external interference, all the Channels in a given Group are known to be compatible with each other. Unless you're using any coordination software, always stick to using different Channels in the same Group.
Let's Bring It All Together
So this is where it can get complicated. Typically, Group 1 always covers the entire tuning bandwidth of the radio mic system. This isn't always desirable, though, as you may only be licensed to operate radio microphones in a specific TV Channel.
Some groups are limited to a specific TV Channel only. For example, Groups 6, 7 & 8 may cover one TV Channel only. In this instance, by tuning separate radio mic systems onto the Channels (spot frequencies) in Group 6, you could get 17 Channels (of wireless microphones) operating in (TV) Channel 38.
Simple, right?! - In hindsight, giving one word three meanings only decipherable in context was a poor choice, but I hope this guide has helped to explain it a little… If not, 'channel' your questions in our direction.